﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Dem
{
    class Program
    {
        static void Main(string[] args)
        {
            const Double π = 3.14;
            Console.WriteLine("请输入圆的半径");
            string str= Console.ReadLine();
            int num = int.Parse(str);
            Console.WriteLine("圆的面积是"+(π*(num*num)));


        }
    }
}
